Gram Positive Cocci: Staphylococci and Streptococci

Gram Positive Cocci: Staphylococci and Streptococci
Bacterial infections are one of the leading causes of death. Two medically important genera of Gram-positive cocci are the Staphylococcus sp. and Streptococcus sp. The two genera are non-motile and non-spore forming. Both are gram-positive cocci which means that they appear purple when stained and are spherical in shape. Although they may look the same, the two may be distinguished from one another. When viewed under the microscope, Staphylococci appear in grape-like clusters while Streptococci appear in long or short chains. Another distinguishing characteristic is the ability of Staphylococci to produce catalase while Streptococci do not.
Staphylococci are responsible for many serious infections, particularly, the S. aureus which causes abscesses, scalded skin syndrome, toxic shock syndrome, boils, osteomyelitis, gastroenteritis, and infective endocarditis. Aside from these, it is also one of the most common causes of hospital-acquired pneumonia, septicemia, bacterial conjunctivitis, and surgical-wound infections. It is an important cause of skin infections, such as folliculitis, cellulitis, and impetigo.
They are normally found in the mucous membranes and skin. Transmission of the pathogen can either be endogenous or exogenous. Contaminations are also commonly found in food where workers do not wash their hands after sneezing. It is found that 20-30% of the population are normal carriers of the bacteria. Aside from S. aureus, Staphylococcus epidermidis can cause endocarditis and prosthetic joint infections. Staphylococcus saprophyticus causes urinary tract infections.
Diagnosis of the bacteria is by Gram stain and culture. Treatment is usually with penicillinase-resistant beta-lactams, but because antibiotic resistance is common, vancomycin or other newer antibiotics may be required. Some strains are partially or totally resistant to all but the newest antibiotics, which include lin...